The evolution of President Abraham Lincoln's thinking about emancipation is clearly marked out in his speeches and public documents. The evolution of his views about suffrage for black people is harder to trace. The two issues are intimately linked, and to modern eyes they seem one and the same. In Lincoln's time, though, the issues of emancipation and suffrage pulled in different directions, and their history is tangled.

Lincoln did not make a public call for the vote for black men until the last few weeks of his life, and even then his proposal was tentative and compromised. But he had been laying the groundwork for something stronger and more sweeping for a long time. How he laid that groundwork, both in the public mind and in his own, says something about how moral changes come about in our country.

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Lincoln entered the Civil War assuming that his paramount responsibility was to restore the Union. Although he was always an opponent of slavery, the promise under which he had been elected was not a pledge to end slavery but a pledge to prevent the admission of more slave states into the Union. It was a policy he believed would compromise the vitality of slavery and ultimately destroy it — and it was a policy Lincoln declined to surrender, despite considerable pressure to do so, as states began to secede from the Union in 1861.

Lincoln understood that the federal constitution of his day did not give him the power to abolish slavery directly, whether by ordinary lawmaking or by proclamation. Only a constitutional amendment, something he was unlikely to gain, could accomplish that end. He did, however, understand that wartime exigencies might make it possible for him to abolish slavery, since the British had used emancipation as a weapon of war against the United States at the time of the revolution, and the French, the British and the Spanish had all used it against each other. But Lincoln was very cautious about using his war powers to abolish slavery. In the first place, he understood that the Supreme Court was dominated by Southern sympathizers. He could not use his war powers to abolish slavery unless emancipation genuinely were required by military necessity. This limited the scope of the emancipation he could proclaim. He could not, for instance, emancipate the slaves in states loyal to the Union, where the war powers argument could not apply. Furthermore, he could not argue merely that emancipation would serve the interest of Union victory but had to argue that the Union could not be restored at all without emancipation.

Lincoln also had to respond to powerful practical constraints. He was wary of testing the loyalty of the four Unionist slave states — Missouri, Kentucky, Maryland and Delaware. In April 1861,the 6th Massachusetts Infantry Regiment was attacked by secessionist mobs as it transferred between train stations in Baltimore while en route to defending Washington, D.C. The regiment had to fight its way out of the city, after which the mayor destroyed the railroad bridges connecting Baltimore to the North. Only Maryland's failure to rise in support of Lee's invasion in September 1862 made Maryland's Unionist loyalty clear.

By then it was clear to Lincoln that there could be no Union without emancipation, and that he, like almost everyone else but Frederick Douglass, had been kidding himself if he believed that the Civil War was about anything other than emancipation. Looking back on his second inaugural address, Lincoln conceded that the understanding of both sides at the beginning of the Civil War had been clouded by self-serving and wishful thinking. The Union had believed that the Civil War was a war about the restoration of the Union and about whether elections could be repealed by force. The Confederacy believed that it was a war about independence and states' rights. But both sides somehow knew, though they did not acknowledge it even to themselves, that the war was ultimately about slavery.

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But when did the burden shift from mere emancipation to equality? The connection between the two issues was extremely fraught. The broadening of the voting franchise in the Jacksonian era was accompanied by a dramatic rise in the intensity of racism. So long as racial inequality was merely one among many kinds of inequality that the society tolerated, racism did not need to assume the especially vicious form it assumed during the long descent to war. But as the franchise broadened, giving the poor white an increasing chance of claiming political equality with the rich white, both the poor and the rich white had a stake in intensifying racial inequality.

The rich white used race to appease the poor white, while the poor white used race to extort acknowledgment from the rich white, a state of affairs George Fredrickson long ago named "herrenvolk democracy." Indeed, as Edmund Morgan showed almost 40 years ago, in the colonial era, the poor white only achieved what freedom he had because the rich white had black people to exploit in his stead. Democracy may contradict slavery, but only slavery made it possible.

Herrenvolk democracy is unstable. The poor white, like Pap Finn in Twain or Ab Snopes in Faulkner, always suspects that the rich white either seeks to subject him as he subjects black people, or seeks to elevate black people at his expense.

Andrew Johnson, the most powerful "poor white" in American politics during Reconstruction, for instance, irrationally feared that the freedmen and their former masters would ally themselves against the white non-slaveholders of the South. The rich white, in turn, could not be certain that, without a great deal of angry manipulation, race loyalty really would succeed in trumping class loyalty and keeping the black and white poor from making common cause.

Because herrenvolk democracy was not confined to the South, Lincoln could not have connected emancipation to the franchise without complicating, and perhaps even foreclosing, emancipation itself. Lincoln faced this for the most part by not facing it; if he had to articulate the future he imagined for the freed slaves publicly, he might never have been able to emancipate them at all. Sometimes he employed strategic indirection, suggesting that freed slaves might allow themselves to be colonized in Liberia, Haiti or Central America. But all of these plans were desultory, and even in Lincoln's first mention of colonization, in his Peoria speech of 1854, it is clear he thought colonization was a brutal and impractical idea.

Lincoln also had to address his own feelings about race. Frederick Douglass reported that he never sensed from Lincoln that visceral distaste for black people that he often sensed from white people, even from abolitionists. But Lincoln felt the force of racism and admitted — modestly in the Peoria speech, somewhat more harshly during the debate with Stephen Douglas at Charleston, Ill., in 1858 — that his own feelings balked at racial equality. But even here, he made concessions to racism because he did not see how to defeat it; racism in Lincoln's mind was a bad but intractable habit, something like alcoholism, something that does not just go away once one realizes that it is destructive. Lincoln addressed popular racism, including his own, with the same delicacy and indirection he had used to keep Maryland in the Union.

When, under pressure from Douglas in their 1858 debates, Lincoln denied having any intention of promoting social or political equality across racial lines, he was probably speaking the truth. But the transformation of his views over the war years was possible because he had long since committed himself to arguments that, whether he acknowledged it or not, could not help but raise the question of racial equality.

In articulating the rationale of the Emancipation Proclamation, the president chose grounds that made clear that emancipation could not be the limit of his intentions. Lincoln's explicit rationale for emancipation was to enable him to recruit freed slaves into the Union Army. This apparently modest argument had the advantage of turning on a bona fide military necessity. Furthermore, unlike the argument about making economic war on the Confederacy, this argument had the merit of making emancipation irreversible. Those you have freed in order to make economic war can be re-enslaved in order to rebuild a peacetime economy. But you cannot re-enslave men into whose hands you have put rifles. In addition, in rejecting the idea of provoking a disabling slave insurrection in the Confederacy as an aim of the Emancipation Proclamation, Lincoln put aside a course of action that would have made it harder for former slaves and former masters to live with each other as peaceful citizens after the war. Most important of all, grounding emancipation upon the idea of recruiting black soldiers made a trumping case for political equality for black men.

In a letter read at a Unionist meeting in Illinois in August 1863 known as the Conkling letter, Lincoln went so far as to contrast what the republic would owe to anti-emancipation Unionists with what the republic would owe to freed slaves who, at risk of life and limb, had saved it with clenched teeth and steady aim. It was black soldiers, far more than white half-hearted Unionists, who proved, in the words of the Conkling letter, "that among free men, there can be no successful appeal from the ballot to the bullet." The Conkling letter does not promise the vote. But it does make clear who deserves the vote and who is unworthy of it; it makes it clear that the black soldiers had put the res publica before their lives while squeamish white Unionists stayed home.

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What Lincoln implied in the Gettysburg address, but did not say in so many words until the Reconstruction speech he delivered only two weeks before his assassination, was that the Civil War was not merely a test of republics' political stability, of whether the minority can always destroy the constitutional order if it does not have its way. Nor was the war a test of the possibility of self-rule, or of the principles of life, liberty and the pursuit of happiness. The key issue upon which the war turned, Lincoln argued in the first sentence of that speech, was equality, for no republic can flourish unless it risks its survival by facing up to what equality requires.

What changed Lincoln's mind and made him ready to make the case for political racial equality? Usually when you change your mind about something deep, it is because you realize that the new view does better justice to your core values than the view you are leaving behind. Our key ideas are always larger than our compact statements of them can render. They have inexhaustible implicitness: They commit those who honor them to entailments they could not have anticipated when the commitments were made — entailments that sometimes were even explicitly denied.

When Thomas Jefferson wrote that it was a self-evident truth that all men are created equal, he both did and did not will the end of slavery. Lincoln, making similar arguments in the early years of the Civil War, both somehow knew, and did not publicly acknowledge, that the promise of equality is a promise of racial equality. The meaning of the promise of equality continues to become clearer even today, and its furthest implications have yet to be brought to light. Few of those implications could have been in the focal consciousness of the Founding Fathers or Lincoln. But to deny being bound by the entailments of such values is probably a more destructive misreading of the founders' intentions than to acknowledge being bound by them. Both Lincoln and Jefferson were in a position to deny embracing those intentions, and their denials may not have been entirely strategic.

Consider: Even while Lincoln was still denying any intention of seeking racial equality, the values that would later commit him to that course were already at work. In 1858, for instance, Lincoln and Douglas were engaged in a furious debate over the future of Kansas Territory. Neither man wanted slavery to go into Kansas, although for different reasons: Douglas because the people of the territory did not want it, Lincoln because slavery is wrong in itself. In any case, by the summer of 1858, it was clear that Kansas would not welcome slavery after all. So why should it matter whether Kansas rejects slavery for the right or wrong reasons?

In the first place, there was a practical issue: If slavery were rejected for political rather than for moral reasons, a change in economic or demographic circumstances might well revive interest in slavery. But if slavery were morally stigmatized, its chances of revival would be smaller. That practical issue wasn't what moved Lincoln most crucially. Lincoln was willing to bow to necessity and tolerate slavery where it already existed. But failing to stigmatize slavery would ultimately risk the moral prerequisites for democratic rule, since mastership corrupts the culture of freedom, and slaveholders must seek to dominate the politics of any polity in which they play a part. As Lincoln wrote in an 1859 letter: "This is a world of compensations; and he who would be no slave, must consent to have no slave. Those who deny freedom to others, deserve it not for themselves; and, under a just God, can not long retain it." Slaveholding debauches the public mind out of the conviction that all men are created equal; no democracy can long survive the loss of that conviction.

A purely political case does not have racial equality as an implication, since it's not in the nature of a majority to seek rights for minorities that the majority has an interest in exploiting. Lincoln repeatedly and plausibly denied having an investment in racial equality when Douglas accused him of it, and in the tangle of his complicated motives and necessities, I would hesitate to say that he had a mature plan for racial equality. But racial equality was within the penumbra of his intentions, a course of argument he had chosen even while recognizing that this course had a political cost (a cost that included his defeat in the close Senate election in 1858).

Implicit commitments like these, only darkly understood even by those who made them, have the kind of depth that makes it an open question whether they are expressions of conscious agency or the unchosen and inevitable realizations of character and destiny. The force of an implicit commitment was not something felt by Lincoln alone; indeed, part of the course of American history has been the unfolding of new responsibilities made evident to us by a deeper understanding of values — values that are expressed and betrayed under the pressures of political and historical circumstances. That emancipation should lead to suffrage seems obvious in retrospect because connecting them does better justice to the value that underlies emancipation — a sense of the moral equality of all persons — than separating them does. That suffrage for black men should lead to suffrage for women likewise seems inevitable in retrospect, however different the two causes may have seemed to some at the time. That equality among genders should imply equality among sexual orientations seems just as inevitable, however impossible it might have seemed only a year ago.

We do not always understand the meaning of our deepest moral commitments when we make them, because we see them through the haze of our limitations and from within the double-binds of our time and place. Sometimes we explicitly deny what in retrospect seem to be the implications of our own words. As exigencies force us to re-examine our values' meaning, new layers of obligation are required. Our constitution changes because under the pressure of moral crisis we come to understand its underlying values better than we did before. Whenever we have achieved a fresh grasp upon the meaning of democracy, we have done something that seemed impossible beforehand, although once we have done it, our chief question becomes, What took us so long to get around to it? In serving those old values in a new way, we show more loyalty to the founders than we would have shown had we confined ourselves to what was in their focal intention in their time (assuming we are in a position to know that), because what was in their focal intention was always an imperfect, even a distorted, reflection of what most mattered to them. It is only when we have thought anew — and acted anew — that we have disenthralled ourselves and saved our country. But in doing that we have shown why, despite everything, it was and is the last best hope of earth.

John Burt, a professor of English at Brandeis University, is the author of "Lincoln's Tragic Pragmatism."